After I had my third child, I had gained an excess of 40 pounds. I was not very successful about diet, nor was I successful at losing weight somewhere else. What I had was a treadmill. I would run 5 miles on that thing for five days a week. I wasn't dieting. I also wasn't over-eating. The combine effect of treadmill running and eating just the right amount of food for me made me lose all the weight I've gained. I was a size 8, and shrunk all the way to size 2 after 6 months.
My husband is big on getting treadmill with good ratings. He'd research for months before making a decision to buy. TreadmillsGuru seem like a good place to check out ratings on different treadmills.